1. Field of the Invention
This invention relates to a topsheet or cover material for absorbent articles or materials, for example, feminine care products such as sanitary pads or napkins, and the like, surgical drapes, fenestration reinforcement, absorbent pads and similar materials. More particularly, this invention relates to apertured film covers which provide rapid fluid intake and low cover staining compared to conventional cover materials.
Films have been traditionally used to provide barrier properties in limited use or disposable items. By limited use or disposable, we mean that the product and/or component is used only a small number of times, or possibly only once, before being discarded. Examples of such products include, but are not limited to, surgical and healthcare related products such as surgical drapes and gowns, disposable absorbent pads used, for example in the meat industry, and personal care absorbent products such as diapers, training pants, incontinence garments, sanitary napkins, bandages, wipes and the like.
In protective apparel, such as hospital gowns, films are used to prevent cross exchange of microorganisms between the wearer and the patient. Although these films are generally effective barriers with respect to water vapor and the like, they are not aesthetically pleasing because their surfaces are smooth and either feel slick or tacky, and they are visually unappealing, making them less desirable in apparel applications and other uses where they are in contact with human skin. A primary purpose of the film in such laminates is to provide barrier properties. However, there is also a need that such laminates be fluid transmissive so that they can transmit fluids in a direction away from the fluid source. Similar requirements exist for absorbent materials such as absorbent pads used, for example, in the meat industry and absorbent materials used for fenestration reinforcement.
2. Description of Prior Art
Most absorbent articles include a cover material, an absorbent core, and some type of backing material which is generally liquid impervious to help prevent leakage. Types of cover materials generally fall into two main groups based, at least in part upon performance and aesthetic preferences. In the area of feminine care and sanitary napkins, the market is polarized into two segments, women who prefer clean and dry apertured film covers and women who prefer soft, cloth-like nonwoven covers. The advantage of apertured film covers for sanitary napkins is that they provide a relatively clean and dry surface as menses or menstrual discharge tends to pass through the apertured film layer and into the interior of the absorbent product. A drawback, however, is that such apertured film layers do not provide the degree of softness and comfort that a nonwoven cover material can provide. An additional drawback is the smooth, slick, non-cloth-like feel that is characteristic of many apertured films. Nonwoven-based cover materials, on the other hand, are very soft and cloth-like in feel but tend to retain more of the menses at or just below the surface of the cover material which, in turn, makes the product suffer from the standpoint of properties such as cleanliness and dryness. The difference in functionality is a direct result of the structure of nonwovens, including small average pore size and nonuniform pore size distribution.
Cover sheet materials are utilized for the transport of bodily fluids into the absorbent core of personal care absorbent articles and, thus, materials used for cover sheet applications must manage distinctly different body excretions, depending upon the application and the product type. Some products must manage fluids, such as urine, while others must manage viscoelastic fluids, such as menstrual discharge and fecal matter. The management of viscoelastic menstrual discharge by cover sheet materials for feminine care products is exacerbated by the variations in composition and rheology over a broad range of elasticity. Fluid management in feminine care applications requires control of absorption of bodily fluids, control of fluid retention in the cover, control of stain size and intensity, control of rewet of fluid back to the surface, and control of the release of fluid to the absorbent core.
There are basically three major classes of cover systems which have been developed to manage these fluids: nonwovens, apertured films, and composites of films and/or nonwovens. The characteristics of an ideal cover system include the capability of immediate fluid intake, no rewet of fluid back to the surface, no fluid retention in the cover, non-staining, and complete desorption of the fluid to the absorbent core.
Apertured film covers have been defined in the art for use in feminine care applications. Much of the art teaches the use of hydrophobic polyolefin film covers comprised of polyethylene as the base sheet. One drawback of these covers is that they tend to have poor fluid intake unless the pore diameter is large. However, as the pore size increases, the cover will have a tendency towards higher rewet and may detract from visual signal to the consumer. Also known in the art is the use of hydrophilic treatments which are topically applied to the surface to promote rapid fluid intake. However, these cover materials tend to display high rewet high fluid retention, and a lot of staining. Thus, an optimal cover is one that has rapid fluid intake coupled with low cover staining and fluid retention. One means for attaining this feature is an apertured film having wettable apertures and a hydrophobic top surface. Numerous means for attaining this feature are described in the prior art, but most of these means are unfeasible to process commercially, fugitive in nature, not regenerative, lacking control as to surfactant location, or limited to surfactant types. See, for example, U.S. Pat. No. 4,755,413 and U.S. Pat. No. 4,820,294 to Morris which teach an apertured plastic film wherein the edges of the apertures are coated with a hydrophilic material and a method of manufacture in which the apertures are formed by pin aperturing and the hydrophilic material is applied to the edges of the apertures as the pins are withdrawn. Because the hydrophilic material is applied in this manner, it is not possible to accurately control the final disposition of the hydrophilic material on the apertured plastic film. See also, U.S. Pat. No. 4,735,843 to Noda. This invention defines a simple means for attaining an apertured film with apertured regions of a higher surface energy than the top surface as well as a means for controlling and maintaining the surface energy or the distribution of surface energy in the pore or on the surface.
It is one object of this invention to provide a method for producing apertured film covers for use in a fluid absorbent material such as feminine care products, surgical drapes, fenestration reinforcement, absorbent pads and the like having aperture regions having a higher wettability than at least a portion of the top surface thereof.
It is another object of this invention to provide a method for producing apertured film covers for use in a fluid absorbent material which provides a means for controlling the surface energy (wettability) or the distribution of surface energy in the apertures and/or an area of the film cover immediately surrounding the apertures and/or on the surface of the film cover.
These and other objects of this invention are achieved by a method for producing a film cover for use in a fluid absorbent material comprising the steps of forming a polymeric film having a surfactant reservoir, a top planar surface and a bottom planar surface and forming a plurality of apertures in the polymeric film whereby at least a portion of the apertures have an aperture region having a higher surface energy or wettability than at least a portion of the top planar surface of the polymeric film. In accordance with one preferred embodiment of this invention, the polymeric film comprises a plurality of layers, at least one of which comprises a polymer selected from the group consisting of virgin polymer, polymer blends, copolymers, polymers with fillers, polymers with additives, and mixtures thereof and another of which comprises a blend of a polymer selected from the group consisting of virgin polymer, polymer blends, copolymers, polymers with fillers, polymers with additives, and mixtures thereof and a plurality of pellets, which plurality of pellets are formed by internally compounding at least one surfactant into a polymeric resin and extruding the polymeric resin into pellets.
In accordance with one embodiment, the polymeric film comprises a plurality of layers, at least one of which comprises a polymer selected from the group consisting of virgin polymer, polymer blends, copolymers, polymers with fillers, polymers with additives, and mixtures thereof and another of which comprises a polymer selected from the group consisting of virgin polymer, polymer blends, copolymers, polymers with fillers, polymers with additives, and mixtures thereof and at least one surfactant, which is added by direct addition to a melt during processing.
Suitable means for aperturing of the polymeric film include pin aperturing, slitting and stretching of the polymeric film, and vacuum aperturing. Aperturing in accordance with the method of this invention produces a plurality of apertures, each of which comprises a peripheral wall, or flap, around at least a portion of a periphery of each aperture, which peripheral wall extends from a bottom surface of the polymeric film.
In accordance with one embodiment of this invention, the polymeric film is formed from a polymeric material comprising a plurality of spheres, or microcapsules, of a surfactant and the apertures are formed by electric discharge means or mechanical means whereby the spheres of surfactant are ruptured, thereby rendering edges of the apertures wettable.